you need to get the business first!
How you go about employing people comes second, but I would have thought that getting part timers in will be tough going. The weather isn't going to have a big effect, you lose a day here and there, big deal, it goes with the territory.
The problem with employing people is paying out Employers liability, Employer NI contribututions and don't forget you have to pay their tax too!
You can write what you like in a contract, but for what you are talking about the tax man will consider them employees if they get to here of it and its no use squawking about the clever small print you have put in the contract that you might think will absolve you!!
Regards,
Ian